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Date :- 28th October 1941
Ref : - AFDU/3/19/44
TACTICAL TRIALS - Me.109F AIRCRAFT
... and the aircraft was dived at 420 indicated and the aileron control still found to be quite good, though considerably heavier. Elevators quite good but not very light.
7 . No manoeuvrability trials were carried out against other aircraft but the Me.109F was dived up to 420 m.p.h., I.A.S., with controls trimmed for level flight and it was found that altough the elevators had become heavy and the ailerons had stiffened up appreciably, fairly tight turns were still possible.
We cannot make a blanket statement that either aircraft design is superior to the other in horizontal maneuvering.
As I understand, low control forces are advantagous for high instantanous manouvers
Confused Kurfurst?This is tactical advise to the RAF Spit pilots, how to get around the negative G problems with a roll-and-dive manouvre. Seems to me exactly the same content as the German manual.
Hi Al,
>Technical Instructions of the Generalluftzeugmeister, Berlin, 28th August 1942.)
Thanks a lot! Where did you find this gem?
Let me try to re-translate this sentence since there is a slight inaccuracy in the above translation:
'Dive: Adjust trim so that the aircraft can be held in the dive by pushing on the stick. The elevator forces and tailplane loads become very high at high indicated airspeeds. The friction brake of the tailplane adjustment drive has to work flawlessly, else the tailplane can change incidence by itself [driven by the aerodynamic loads].'
That's interesting, too. ('Maximum permissble dive speed 750 km/h. Harsh aileron deflection in the dive and especially on pull-out leads to airframe failure.')
I found a description of this effect (caused by wing warping induced by the aerocdynamic forces on the ailerons) in Mike Crosley's "Up in Harm's Way" - he was a Seafire pilot in WW2 and a test pilot after the war, and they found that aileron-induced wing failure was a reason for some then unexplained losses they had in the war.
I have always suspected that the Messerschmitt must have suffered from the same problem as it has the same single-spar wing construction as the Spitfire, but I couldn't find anything definite on this topic before, so thanks for confirming my suspicion!
QUOTE]
HoHun - It was mentioned IIRC in Wagner's Mustang Designer or Gruenhagen's Mustang - I'll have to check. Both the 109 and Spitfire, (until the Mk XIV )had situations where the high aero loads on the ailerons caused the wing to torque (i.e the 'down' aileron caused a local twist changing the effective angle of attack to increase) The effect was twofold depending on speed and load - either neutralize or reverse the desired manuever or over stress the wing.
The 51 wing failures mentioned above by Crumpp had two root causes -
1.) the original design for wheel cover uplock failed at very high speed dive and the gear dropped, creating an immediate and fatal wing failure, and 2.) the ammo cover door in a high speed pullout deflected to unexpected point creating a local aeroynamic 'lift' at a critical point in the spar.
Both were fixed with the kits and TO's mentioned by Crumpp
The 51 also had some structural failures associated with rolls in dives. Both the horizontal stabilzer and tail had been designed with pre-war conventional methodology and was simply in adequate for the .80 dive with any aileron and rudder loads to add to the stress in the vertical stabilizer spars.
Not even the beefed up Horizontal stabilizer, metal elevators and tail design changes including reverse rudder boost tab and ventral fin and change in spar and rudder heighth fully solved the issues at those speeds - but the wheel door uplock kits and stiffened ammo doors fully solved the wing failure problem.
The H tail allowed the permissable max dive speed to increase slightly but even it required increasing and dangerous rudder input at max dive to keep from yawing too much.
I've often wondered whether the 109 was more or less of a problem in a similar way as many of the encounter reports talk about tail failures in the chased 109s during high speed dive...
PS - the information contained about the Spit and 109 aileron/wing twist issues were anecdotal but seem supported by the repective Manual discussions above.. I can personally vouch for the 51 in dive but I never pushed it to limit dive.. and the 51 Book is equally instructive about NOT using elevator trim to pull out of a dive.
Regards,
Bill
Hi Bill,
We cannot make a blanket statement that either aircraft design is superior to the other in horizontal maneuvering.
Certainly we cannot make a blanket statement as to specific performance. We can however predict general trends but only as to what the engineering will allow. We also have no method to factor the effects of pilot skill.
Wing structures are akin to a 'tuning fork' extending from the fuselage. When a tuning fork is tapped the fork vibrates at a particular frequency, the stiffer the structure the higher its 'natural' frequency. The natural frequency of a wing or tailplane structure may apply another limiting airspeed to flight operations – related to structural instabilities: flutter and wing divergence.
When the airflow around a wing or control surface is disturbed by aerodynamic reactions, turbulence or pilot inputs, the structure's elastic reactions may combine as an oscillation or vibration of the structure (possibly evident just as a buzz felt in the controls) which will quickly damp itself out at normal cruise speeds. At some higher speed — the critical flutter speed — where the oscillations are in phase with the natural frequency of the structure the oscillations will not damp out but will resonate, rapidly increasing in amplitude. (Pushing a child on a swing is an example of phase relationships and amplification). This condition is flutter and, unless airspeed is very quickly reduced, the severe vibrations will cause control surface [or other] separation within a very few seconds.
Wing divergence refers to a state where, at the very low angles of attack of high speed where the nose-down pitching moment is already very high, pressure centres develop pushing the front portion of the wing downward and the rear portion upward. This aerodynamic twisting action on the wing structure, while the rest of the aircraft is following a flight path, further decreases the aoa and compounds the problem; finally exceeding the capability of the wing/strut structure to resist the torsional stress and causing the wing to separate from the airframe – with no warning! This could be brought about if a down gust is encountered at high speed.
Both were fixed with the kits and TO's mentioned by Crumpp
Hi Kurfürst,
...
However, the Bf 109 and the Spitfire with their single-spar wings were more sensitive against this than other WW2 aircraft. That both lose aileron effectiveness at high diving speeds is the first sign of wing twisting - for the Spitfire, Crosley points out that above some speed, the aileron response actually reversed.
Regards,
Henning (HoHun)
As laborious as that process was I wonder how far the computer modelling has progressed in combining aerodynamic predictions in say, a relaxation methodology, with the matrix decompositions of flight mechanics - and then progress to account for aerdynamic deformations from limit to ultimate loads?